Radiation Talk March 2011 rn

8/6/2019 Radiation Talk March 2011 rn

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Notes for talk on RADIATION (RN)

The recent Japanese earthquake and tsunami has drawn attention and concern around the world,particularly with regard to possible exposure to radiation following damage to nuclear power plants.

The atom and radioactivity

The nucleus or centre of atoms are composed of protons and neutrons. Around the nucleus there areelectrons moving in orbit, similar to the planets around the sun.

The number of protons determines the nature of the atom eg all carbon atoms contain 6 protons, all cobaltatoms contain 27 protons. The number of neutrons in an atom's nucleus can vary, thus varying the atomicweight, giving rise to isotopes. Some nuclei are unstable, but become more stable by emitting portions of thenucleus over time radioactive decay.

Radioactivity is thus the by product of the fact that not all atomic nuclei are stable.

Unstable nuclei decay or transform into more stable nuclei with the emission of radiation in various formsincluding alpha particles, beta particles and gamma rays.


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Types of radioactivity

Alpha decay is a type of radioactive decay in which the nucleus emits an alpha particle a particle

that consists of two protons and two neutrons bound together (the alpha particle is the nucleus of the

stable helium atom). The alpha particle is emitted with an energy that is characteristic of the nucleus

undergoing the decay. Alpha decay mainly occurs only in nuclei with more than 82 protons.

eg Plutonium-239 -> uranium-235 + alpha particle

The radioactive half life of the above decay is about 24000 years plutonium-239 is

therefore a very long-lived isotope.

Beta decay is another type of decay in which either a neutron is converted to a proton and the

nucleus emits an electron, or a proton is converted into a neutron and the nucleus emits a positron (a

positively charged electron).

Iodine-131 -> Xenon-131 + beta particle (electron)

Sodium-22 -> Neon-22 + beta particle (positron)

Gamma rays: the nucleus of an atom may have several different energy states. Higher energystates (sometimes called excited nuclei) tend to decline to lower energy states. They do thus by

emitting energy in the form of gamma rays.

Ionising radiation

Ionising radiation consists of particles or electromagnetic waves that are energetic enough to

detach electrons from atoms or molecules, thus ionising them. Direct ionisation from the effects of single

particles or single photons produces free radicals (atoms or molecules containing unpaired electrons), that

tend to be especially chemically active, thus may result in damage to DNA and to the cells of the body.

The degree and nature of such ionisation depends on the energy of the individual particles (includingphotons), not on their number (intensity).

Examples of ionising particles are alpha particles, beta particles, neutrons, and cosmic rays. The ability of

an electromagnetic wave (photons) to ionise an atom or molecule depends on its frequency, which

determines the energy of its associated particle, the photon.

Radiation on the short-wavelength end of the electromagnetic spectrumhigh-frequency ultraviolet, X-rays,

and gamma raysis ionising, due to their composition of high-energy photons.

Lower-energy radiation, such as visible light, infra-red, microwaves, and radio waves, are not ionising.

How may ionising radiation cause harm?

Ionising radiation may cause harm in two ways. First by slow incremental exposure over many months or

years, with an increase in the risk of developing cancer or leukaemia. Secondly, by a higher exposure in a

short period of time of minutes or several hours.

Ultraviolet radiation, found in sunlight, is well known as being potentially harmful. We all know that slow

exposure of the skin results in tanning, while acute exposure results in sunburn. Over the years repeated

skin exposures result in changes to the skin ageing, solar keratoses, and perhaps cancers such as SCC,

BCC or melanoma.

Similarly, other forms of ionising radiation may cause harm to the body, including X-rays, gamma rays, alpha

particles and beta particles.

In brief, when radiation interacts with matter (in particular living tissue), the main effect is to remove the outer

electrons of the constituent atoms by ionisation. The result is that a number of free electrons are created,


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and a number of positively charged ions are created. The free electrons and ions to recombine to give a

neutral atom once again. Some of the free electrons may be sufficiently energetic to cause ionisations of

their own. It is this process of ionisation that is responsible for the biological damage that can be caused by

radiation.

How is ionising radiation detected?

It is important to realise that the human senses do not respond to ionising radiation at all. To prevent harm,

we must be able to detect, identify, and measure radiation. To prevent overexposure, and to minimise doses,

radiation measuring instruments must be used. A practical instrument must tell us which type of radiation it

is measuring, as well as the intensity. All radiation measuring instruments have a detector in which the

radiation deposits energy.

Unfortunately, all radiation detectors respond to more than one type of radiation so instruments have to be

designed such that only the effects of the kind of radiation we are trying to measure are recorded. Generally,

in mixed radiation fields, a number of different instruments is required to measure the intensity of each

radiation present.

When ionising radiation passes through a gas it creates ion pairs, leaving a trail of electrons and positive

ions in its wake. One method of measuring radiation is to collect the ions produced. The Geiger counter

works in this way.

Measuring ionising radiation dose

One of the earliest observed properties of X-rays was their ability to ionise air. In 1928 this property was

specified as a means of measuring the amount of X-radiation. The unit of measurement was named the

roentgen, after Professor Roentgen who discovered X-rays

Different materials and tissues absorb ionising radiation to different degrees - the absorbed dose. The unitfor absorbed dose is called the Gray (Gy).

The same absorbed dose delivered by different types of radiation may result in different degrees of biological

damage to body tissues. The equivalent dose was introduced to take into account the dependence of the

harmful biological effects on the type of radiation being absorbed.

The equivalent dose is therefore a measure of the risk associated with an exposure to ionising radiation .

Risks due to exposures to different radiation types can be directly compared when in terms of equivalent

dose. The unit of equivalent dose is the Sievert (Sv).

How much ionising radiation is harmful?

Shortly after the discovery of X-rays in 1885 by Professor Roentgen, scientists began to notice their harmful

effects. It was, however, many years before people realised how dangerous x-rays and other radiations could

be. The older in the audience may remember how X-Ray viewers were used in shoe shops with claims that

their use provided better fitting shoes!

Quite a number of pioneer radiologists suffered severe injuries (some even died) as a result of prolonged

exposure to dangerously high intensities of X-rays. These early workers in the field had no means of

measuring the harm caused by radiation accurately and depended on unreliable effects such as the degree

of skin reddening caused by the exposure, or on timing the exposure from a certain type of X-ray machine to

establish quantity.

The short answer to the question is we do not know how much ionising radiation is harmful. It is safer to

assume all ionising radiation is potentially harmful, to exercise discretion as to when it should be used, in the

lowest possible doses to achieve the desired outcome.


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Background radiation

Each of us is exposed to cosmic radiation, as well as radiation from our surroundings, including the soil, the

stones and bricks of our homes and the foods we eat. This is called BACKGROUND RADIATION. On

average, each person worldwide receives 2.4 mSv per year. In some places like the Rocky Mountains and

the Flinders Ranges, the dose from the ground is higher. The highest is in Iran, in the region of Ramsar

260mSv per year.

Every square mile of surface soil, to a depth of 6 inches (2.6 km2 to a depth of 15 cm), contains

approximately 1 gram of radium, which releases radon in small amounts to the atmosphere. Radium is

found in uranium ores in trace amounts as small as a seventh of a gram per tonne of uraninite.

Uranium occurs naturally in low concentrations of a few parts per million in soil, rock and water. It is

commercially extracted from uranium-bearing minerals such as uraninite. In nature, uranium is found as

uranium-238 (99.2%), uranium-235 (0.7%), and a very small amount of uranium-234 (0.005%). Uranium

decays slowly by emitting an alpha particle. The half-life of uranium-238 is about 4.47 billion years and that

of uranium-235 is 704 million years, making them useful in dating the age of the Earth.

Radon

The gas Radon is formed as part of the normal radioactive decay chain of uranium. Radon is responsible for

the majority of the public exposure to ionising radiation. It is often the single largest contributor to an

individual's background radiation dose, and is the most variable from location to location. Radon gas from

natural sources can accumulate in buildings, especially in confined areas such as attics, and basements.

Radon is considered a significant contaminant that affects indoor air quality worldwide.

According to the United States Environmental Protection Agency, radon is the second most frequent cause of

lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the United States (as an

aside, tobacco smoke itself is a well known cause of cancer, containing chemical carcinogens as well as

small amounts of radioactive lead and polonium).

Examples of other doses from radiation

A single chest XRay gives 0.06 mSv

a mammogram 3 mSv

a CT scan of the chest 5 mSv.

Sleeping next to someone results in 0.00005 mSv

eating a banana 0.0001 mSv

Flying from Los Angeles to New York or from Cairns to Perth 0.04 mSv

Ionising radiation and cancer

A dose of 100 mSv ionising radiation is considered significant, causing perhaps one additional cancer per

100 people exposed, of whom 42 will develop cancer from other causes including genetics, diet and

unknown. This can be assessed only in large population surveys of 100,000 people, such as were exposed

at Hiroshima and Nagasaki in WW2.

A large dose in a short time of seconds, minutes or several hours may cause acute radiation poisoning. An

acute dose of 500 mSv may result in nausea. Internal haemorrhaging may start after an acute dose of 1000

mSv. With an acute dose of 5000mSv, half of those exposed die within 30 days, while after 20,000 mSv aperson may die within hours or several days.


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Radiation protection

A worker in a nuclear power station or those who work with radiation including radiographers and radiologists

are limited by law to an annual dose of 20 mSv per year over 5 successive years, or 50 mSv in a single year.

By law, a receptionist or non-technical staff member of an XRay Dept should not receive more than 1 mSv

per year from their working environment. This dose limit also applies to ordinary members of the public, who

may visit an Xray Department accompanying family members who are having tests.

Fukushima, Three Mile Island and Chernobyl

The largest dose to an individual worker so far recorded in the Japanese nuclear power station has been

106mSv. Since then the occupational dose limit for the 180 or so workers at Fukushima has been raised to

250 mSv because they are deemed to be working in a life saving situation. They should be regarded as

heroes.

The Japanese reactor has emitted small amounts of radioactive iodine, I-131, which has a half life of 8

days. Iodine by mouth can limit the uptake by the thyroid gland but should only be taken on prescription, as

allergies are possible.

Caesium-137 is of greater concern, having a half life of 30 years. There are large amounts of Caesium in

and around Chernobyl, even 25 years after the melt down there.

Other isotopes which are of potential concern are Strontium-90 and Plutonium (the latter lasts thousands of

years)

Nuclear reactors also emit other radioactive gases but these isotopes are mostly very short lived, decaying

totally in a second or less, thus not harmful to the general population.

Beyond Fukushima at 50 km NW of the power station the largest one day dose recorded was 3.6mSv, on 16

March and again on 17 March. This is equivalent to one year of background radiation for those living in the

USA. On 16 March the maximum readings within the grounds of the power station peaked at 10.85 mSv /

hr .

Radiation exposure of up to 0.17 mSv per hour has been reported up to 30 km (19 miles) away from the

damaged nuclear reactors. This is within the 20 to 30 km "stay in your house" zone. Experts say exposure to

this amount of radiation for 6 to 7 hours would result in absorption of the maximum level considered safe for

one year for a member of the public, or 1/50 th of the maximum allowable dose for a radiation worker (not

working in an emergency).

The Three Mile Island event has resulted in an estimated additional exposure to members of the public of

0.08 mSv per year (a nuclear power station under normal operations may emit only 0.25 mSv per year).

The Chernobyl nuclear plant accident occurred 25 years ago on 26 April 1986. Those spending 10 minutes

next to the Chernobyl reactor received 50 Sv (50,000mSv), consequently developing acute radiation

poisoning or sickness. In the aftermath of the accident, 237 people suffered from acute radiation sickness, of

whom 31 died within the first three months. More than fifty deaths are directly attributed to the accident, all

among the reactor staff and emergency workers. Estimates of the number of deaths potentially resulting from

the accident vary enormously; the World Health Organization suggest it could reach 4,000. The Chernobyl

accident has resulted in continuing and substantial decontamination and health care costs.

Four hundred times more radioactive material was released from Chernobyl than had been by the atomic

bombing of Hiroshima. However, compared to the total amount released by nuclear weapons testing duringthe 1950s and 1960s, the Chernobyl disaster released 1/100 th to 1/1000th the amount of radioactivity.


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Atomic bombs

On Monday, 6 August, 1945, at 8:15 AM, the nuclear bomb "Little Boy" was dropped on Hiroshima by an

American B-29 bomber, the Enola Gay, directly killing an estimated 80,000 people. By the end of the year,

injury and radiation brought total casualties to 90,000140,000. According to the U.S. Department of Energy

the immediate effects of the blast killed approximately 70,000 people in Hiroshima. Estimates of total deaths

by the end of 1945 from burns, radiation and related disease, the effects of which were aggravated by lack of

medical resources, range from 90,000 to 166,000. Some estimates state up to 200,000 had died by 1950,

due to cancer and other long-term effects.Another study states that from 1950 to 2000, 46% of leukaemia

deaths and 11% of solid cancer deaths among bomb survivors were due to radiation from the bombs, the

statistical excess being estimated to 94 leukaemia and 848 solid cancers.

The second bomb was dropped on Nagasaki on 9 August 1945. Within the first two to four months of the

bombings, the acute effects 60,00080,000 in Nagasaki, with roughly half of the deaths occurring on the first

day.

Double A-bomb survivors People who suffered the effects of both bombings are known as nij

hibakushain Japan. Tsutomu Yamaguchi (19162010) as a double hibakusha. He was confirmed to be3 kilometres from ground zero in Hiroshima on a business trip when Little Boy was detonated. He was

seriously burnt on his left side and spent the night in Hiroshima. He arrived at his home city of Nagasaki on

August 8, a day before Fat Man was dropped, and he was exposed to residual radiation while searching for

his relatives. He was the first officially recognised survivor of both bombings. Tsutomu Yamaguchi died on

January 4, 2010, after a battle with stomach cancer at the age of 93. The 2006 documentary Twice

Survived: The Doubly Atomic Bombed of Hiroshima and Nagasakidocumented 165 nij hibakusha.

We should not forget a small number of POWs were among the survivors.

The public response to the reactor problems in Japan

Terminology has caused problems in reporting events at the Fukushima nuclear plant. There have been

references to normal radiation dose without explanation of what that actually means.

There have also been confusion between microSieverts (uSv) and milliSieverts (mSv). 1 Sv = 1000 mSv =

1,000,000 uSv. In this talk I have tried to reduce confusion about doses by always quoting them in

milliSieverts (mSV).

The public lacks factual knowledge about radiation, resulting in fear. This is compounded by distrust of

government and official spokesmen, and the spreading by some of conspiracy theories.

Most people are aware that the effects of ionising radiation cannot be detected by the human senses untilafter it is too late.

Benefiting from the use of ionising radiation

Ionising radiation used in diagnostic medical imaging (radiology) and treatment of cancers has

conferred many benefits.

Ionising radiation is used in certain industrial processes, checking welds etc

Nuclear energy is used to produce electricity with no emissions of carbon.

It can be argued that the availability of nuclear weapons may have resulted in relative peacebetween the major powers since WW2.


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Acute Radiation Sickness develops when

the radiation dose is high (doses from diagnostic medical procedures such as chest X-rays are

too low to cause ARS; however, doses from radiation therapy to treat cancer may be high enough

to cause some ARS symptoms),

the radiation is penetrating (that is, able to reach internal organs),

the persons entire body, or most of it, receives the dose, and

radiation is received in a short time, usually minutes.

To recap (putting ionising radiation into perspective)

A single chest XRay gives 0.06 mSv

a mammogram 3 mSv

a CT scan of the chest 5 mSv, total body CT may result in 30mSv unless low dose techniques are used

Sleeping next to someone results in 0.00005 mSv

eating a banana 0.0001 mSv.

Flying from Los Angeles to New York 0.04 mSv

biggest dose received so far at Fukushima by an individual 106 mSv

annual maximum yearly dose for a radiographer or radiologist 50 mSv

annual maximum dose for a member of the public 1 mSv (10,000 bananas eaten in a year)

annual average background dose 2.4 mSv to each of us (unavoidable) the largest one day dose

recorded in Japan some km from the reactors has been 3.6mSv

acute radiation poisoning requires an acute dose of at least 500-1000 mSv before symptoms develop

in some areas, unprotected workers at Chernobyl received fatal doses within minutes.

Note - of 440,350 wild boar killed in the 2010 hunting season in Germany, over 1,000 were found to be

contaminated with levels of radiation above the permitted limit (600 Becquerel), due to residual

radioactivity from Chernobyl

a little radiation in small doses may actually be good for life. Life forms may be enabled to evolve

due to changes in DNA, induced by non avoidable background environmental radioactivity.

Dose

The word dose has been used frequently in this presentation. This is quite appropriate. Radiation is

potentially beneficial at tiny to lower doses, may be used to treat cancers at higher doses, may cause acute

radiation sickness (ARS) at high doses, and will cause ARS at even higher doses. Much the same as

applies to chemical medications, accuracy and knowledge of dose is essential when using radiation, to

maximise benefit and avoid harm.

The use of ionising radiation should be considered as a prescription when used for medical purposes, just as

drugs used as medications are available on prescription.


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In chart form

RN March 2011

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Radiation Talk March 2011 rn